There are a variety of situations in which it is necessary to make careful, minute adjustments of the amount by which a member protrudes radially outwardly from a rotatable shaft. One such situation is encountered in a boring operation in which one or more tool bits are mounted on and protrude radially outwardly from a rotatable boring bar. The boring bar is aligned within a cylindrical aperture in a work piece and then rotated. The tool bit(s) cut into the work piece, removing material therefrom, to enlarge the aperture. The amount of material removed from the work piece depends upon the displacement between the tip of the tool bit(s) and the longitudinal axis of the boring bar. This displacement must be carefully adjusted to ensure that the correct amount of material is removed from the work piece, leaving a cylindrical aperture of selected diameter in the work piece.
Conventionally, boring machine tool bits are provided in adjustable, calibrated cartridges having threaded outer casings. Typical prior art cartridges are sold by DeVlieg Machine Company of Royal Oak, Mich. under the trademark MICROBORE. A large selection of cartridges of varying lengths and having tool bits with different cutting characteristics are available.
The boring bar is provided with a series of apertures which pass transversely through the bar at selected intervals. A particular boring bar aperture is selected to receive the tool bit cartridge. A pair of opposed keyways are machined into the bar on one side of the selected aperture to mate with a pair of keys provided on the cartridge opposite the tool bit. A cartridge of appropriate length and having an appropriate tool bit is selected and passed through the boring bar aperture so that the cartridge's keys fit within the boring bar keyways. A lock screw threaded through a solid washer is further threaded into the keyed end of the cartridge until the washer butts against the outer surface of the boring bar. The threaded cartridge casing and tool bit protrude through the opposite side of the boring bar. An internally threaded graduated dial ring is threaded over the protruding casing. The cartridge is thus held in place between the washer and the dial ring. The displacement between the tip of the tool bit and the longitudinal axis of the boring bar is adjusted by loosening the lock screw to draw the washer away from the boring bar, turning the threaded dial by the required amount (as determined by indicator marks provided on the dial) and then retightening the lock screw.
The prior art cartridge-based system suffers a number of disadvantages. A considerable amount of preliminary machining must be performed on the boring bar so that it will mate properly with the cartridge. The cartridge may be adjusted only within a narrow range, necessitating the provision of a range of different cartridges to facilitate boring of apertures of different diameters. This represents a potentially significant expense. It is also awkward to adjust the cartridges accurately during the boring operation.
The present invention overcomes the foregoing disadvantages by eliminating the need for multiple tool bit cartridges and by providing a calibrating tool separate from the tool bit holder to facilitate rapid, easy, precise adjustment of the displacement between the tip of the tool bit and the longitudinal axis of the boring bar.